Web break detector



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LJULUL FIP8212 M tMMiN Ln ROSS REFERENCE Oct. 19, 1948.

G. B. DUNN WEB BREAK DETECTOR Filed Aug. 51. 194e .N ...mi

Inventor:

Hi s Attorn ey George B. Duh,

7Patented Oct. 19, 194.8'

WEB BREAK DETECTOR George B. Dunn, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application August 31, 1946, Serial No. 695,339

(Cl. S18- 461) 10 Claims.

This invention relates to devices for detecting breaks in a length of moving material such for example as paper, and it has for an object the provision of a simple, reliable, inexpensive and improved device of this character. Such devices n are known as web break detectors.

scanning means which responds to the indicia on the paper web to produce a. succession of positive voltage pulses together with a photoelectric type selector switch mechanism actuated by one of the printing cylinders for producing a succession of pulses which have a predetermined timed relationship with respect to the pulses produced byv the reference indicia when the operating element is in register with the indicia. The pulses from the web scanning head and thosefrom the selector switch are amplified by separate amplifiers and the amplified pulses are supplied to a mixing valve circuit which detects any 'out of register condition and furnishes a signal of such condition to a register correcting system. This correcting system usually comprises electric valve lcontrol circuits .and a correction motor controlled thereby for restoring the condition of register.

A further object of the invention is the provision of means for detecting breaks in a moving web on which reference indici-a have been printed for use in a register control system.

In rotogravure color register control systems it is generally a specified requirement that the photoelectric scanning heads shall be explosion :proof equipment owing to the highly iniiammable characteristic of the rapidly drying inks which are employed in this process. Explosion proof equipment of this character is very bulky and is also very expensive. Consequently in many installations in which a web break detector is nec- -Aessary or desirable there is no available space `for the additional explosion proof scanner. Consequently, the space factor and the expense of 'such equipment make it desirable to obtain -web break detection and protection without the use 2 of an addition-al scanner. Accordingly, 'a further object of the invention is the provision of a control system which utilizes the photoelectric scanning heads of the register control system for detecting web breaks.

In carrying the invention into eiect in one form thereof, an alarm circuit is provided for a machine which has an element operating upon a length of material having register marks i. e. indicia printed thereon at successive intervals. Means responsive to the speed lof the element 'which operates on the length of material are provided for preparing the alarm circuit for actuation only at speeds in excess of a predetermined value. Photoelectric means responsive to the indicia on the web complete the alarm circuit in response to a breakage of the web as indicated by a decrease in the rate of passage of the indicia at speeds of the operating element in excess of a predetermined value. The alarm circuit may be utilized to give a visual or audible alarm or to disconnect the driving motor of the machine.

For a better and more complete understanding of the invention reference should now be had to the following specification and to the accompanying drawings of which Fig. 1 is a simple diagrammatic sketch of an embodiment of the invention in a web register control system and Figs. 2, 3, and 4 are characteristic curves which serve to illustrate the operation of the invention and to facilitate an understanding of its operation.

Referring now to the drawings, a length of material I such as a web of paper having a color impression 2 printed thereon by printing cylinder 3, travels in the direction of the arrow 4 to a succeeding element operating on the material, illustrated as comprising a pair of printing cylinders 5 which print a, second impression of a different color on the web. It is desired that this second color impression shall be made in exact register -with the first impression which is made by the -cylinders 3. Although only two pair of color vimpression cylinders are illustrated, frequently as many as six pairs are used in practice.

The printing cylinders are driven by suitable -driving means illustrated as an electric motor 6 which is connected to the drive shaft of cylinder '3 by means of suitable gearing and to the drive shaft of cylinders 5 by means of suitable driving connections including the shaft 1.

A mechanical differential device 8 is included in the driving connections between the motor 6 and the cylinders 5. The ring gear 8a of this device Ais driven by a small direct current motor 9 to the drive shaft to which it is connected by means of worm gearing 8b. When the motor 9 is stopped the pairs of cylinders 3 and 5 rotate at equal speed.

The correcting motor receives power from any suitable source under the control of the register control system illustrated in the block diagram of Fig, 1 which comprises the photoelectric web scanner I0, and the photoelectric selector switch I I, the amplifiers I2 and I3, the mixing valve circuit panel I4 and the register correcting apparatus I5. 'Ihe scanning head I0 includes a source of light I6, and a light sensitive device I1 such as a photoelectric cell. This scanning head detects the passage of indicia orregister marks I 8 printed on the web I by the cylinders 3 which print the first color impression. It is connected to the electric valve amplifier I2. Both the scanning head and the amplifier are standard devices which are obtainable on the market. Consefluently, detailed descriptions of these devices are omitted. Itis suicient to understand that when indicia I8 pass the photoelectric cell I1, positive voltage pulses are produced at the terminal IB which are represented dagrarnmatically in Fig. 2 by the successive pulses 2l, 2|, and 22.

A second scanning head comprises a light source `23 and a photoelectric cell 24. This scanning head observes the motion of a disc 25 which is mechanically coupled to the second pair of impression cylinders 5. This disc has a series of Vslits cut in it. The disc has the same number of slits as the number of register marks 'I8 corresponding to one revolution of the impression cylinders Iolution of the disc are satisfactory for web speeds loi 500 to 1,000 ft. per minute. 'These marks and 'slits must be equally spaced to an accuracy equal to or better than that of the error which can be "tolerated A register mark .02 in. Wide in the direction of paper travel and T/z in. long and a disc slit width of 1/4- in. may be used. The lamp 23 projects a beam of light through each slit in lthe disc 25 as it passes between the lamp and the photoelectric cell 24.

'The scanning head II of the selector switch and its amplifier I3 are'standard devices which may be purchased onthe market and accordingly a detailed description of these items is omitted. 'It is suidcient to understand that the chopping V'of the light beam by the slitted disc 25 produces positive voltage pulses at the terminal 2B which "are represented diagrammatically in Fig. 3 by the 4pulses 21, 2B, 29, etc.

Iior the purpose of providing an indication of aweb break, an alarm circuit 30 is provided. The

completion of this circuit s controlled by a web -break detecting device 3| and speed indicating Acontrol system '32. vdetecting device and the speed indicating control system are shown within the dotted rectangles in Fig. 1.

The details of the web break The web break detecting device includes a magnetic control relay 33 having normally closed contacts 33a in the alarm circuit. As shown in the block-diagram, the web register indicia voltage pulses 20, 2|, and '22, etc., at the terminal 'IS are supplied to the web break detector device. Thisbreak detector device maintai'ns the relay 33 energized as long as register `indicia signals are received from the scanning head I0. Theinstant a web breakage occurs reg- 'lster indicia cease to pass under the scanning A1head 'and thus no register mark signals are received.

The yweb break detecting device comprises a For example, 16 marks and slits per rev- CROSS REFERENCE two stage electric valve amplier 34 of which both the first and second stage valves are preferably included within the same envelope. The first stage valve is provided with an anode 34a, a cathode 34h, and a control grid 34e. Similarly a second stage valve has an anode 34d, a cathode 34e, and a control grid 34j. The two valves are supplied from a suitable source of direct voltage which is represented by the two supply conductors 35 and 36.

As shown, the anode 34a is directly connected to the positive supply conductor 35, and the cathode 34h is connected through a resistor 31 to the negative supply conductor 3B. Cathode follower operation of the first stage valve is provided by means of the cathode circuit resistor 31.

The control grid 34e of the first stage valve is connected through a capacitor 38 and conductor 39 to the terminal I9 between the amplifier I2 and the mixing Valve panel I4.

The anode 34d of the second stage valve is connected through the operating coil of the relay -33 and a resistor 40 to the positive conductor 35, and the control grid 34j is cozmected to the cathode 312D of the first stage valve. A voltage divider comprising resistors 4I and 42 is connected across the source 35, 36, and the cathode 34e of the second stage valve is connected to an intermediate point 4Ia of the divider such that the second stage valve is normally biased to cutoff by the cathode bias obtained from the voltage divider. A grid current limiting resistor 43 is included in the connection between the grid 34j and the cathode 34h of the first stage valve.

In the operation of the system the web break detector device 3I maintains the magnetic relay 33 energized as long as register mark signals are received from the scanning head I0 at suiliciently frequent intervals. The instant a web break occurs, 'the register indicia cease to 'pass beneath vthe scanning head and thus no register mark signals are received thereby causing the relay 33 to become deenergzed. The normally closed contacts 33a of the relay then open and shut down the web drive motor, or sound an alarm, or give some visual indication of the break. At zero and very low speeds itis necessary to bypass the web break detector relay because the frequency of the voltage `pulses produced by the reference indicia is so low that the Vsecond stage valve does not remain continuously conducting, and consequently the contacts 433a close. This operation would give a false indication of aweb break when none existed.

The bypassing of the web break detecting device at low speeds is accomplished by means of a pair of contacts 44a Aon a lmagnetic relay 44. These contacts are connected in series Awith the normally closed contacts 33a of relay-33. The relay 44 is controlled by means of the speed indicating device 32 which is operated bythe selector switch signals obtained frcm theV terminal 26 between the amplifier I3 and the mixing valve `circuit I4. As illustrated in Fig. -1 the speed indicating device 32 comprises a two stage eiectric valve amplier. This amplifier is preferably a twin triode electric valve 45. 'The mst stage valve comprises an anode 45a, a; cathode 45h, a control grid 45e, and the secondv stage valve comprises an anode 45d, a cathode'e, and a control grid 45j. The anodes A45a and- '45d are connected to the positive supply conductor 35 and the cathodes '45h and 45e are connected through retors '46 and 41 respectively to the negative supply conductor '36. Cathode follower operation oi. both LHIVIIDILH first and second stage valves is provided by the resistors 46 and 41 in the cathode circuits. In parallel with resistor 46 is a circuit which comprises a capacitor 48, a xed resistor 49 and a variable resistor 50 having a slider v.falla to which the grid 45f of the second stage is connected by means of conductor I.

The capacitor 52 is connected in parallel with resistor 41. The ohmic value of resistor 41 is chosen very large in comparison with the plate resistance of the second stage valve with the result that the discharge time of capacitor 52 is very much longer than its charging time.

The control grid 45c of the rst stage valve is connected by means of a conductor 60 to the` terminal 26 between the selector switch amplier I5 and the mixing valve I4. The signal input to the grid 45e is, as shown in Fig. 3, a positive square wave voltage of which the width or period varies inversely with the speed of the disc 25 and thus inversely with the speed of the printing cylinders` 5. The wave shape of the ampli- 'fied signals appearing at the cathode terminal 46a, is identical with that of the signals supplied to the control grid. The time constant of the circuit including capacitor 48 and resistors 49 and 50 is selected so that the Wave form at the slider 55a is always the same for all speeds below the rated speed of the web. The form of these signals is illustrated in Fig. 4. Each time a positive pulse is received at the slider 50a, the capacitor 52 charges up through the low plate resistance of the second stage valve in a very short time and discharges through the high ohmic value resistor 41 when the pulse has passed. Since the number of pulses received per second Avary directly with the speed of the selector lswitch disc 25 and likewise with the speed of the web itself, the voltage across the capacitor 52 will increase directly with the speed of the web within a predetermined range. The voltage at the cathode terminal 41al is filtered by a resistor 53 and a capacitor 54 and fed into the grid of the rst stage of a phase inverter and amplifier comprising a twin triode valve 55 of which the first stage valve has an anode 55a, a cathode 55h, and a control grid 55C, and the second stage valve has an anode 55d, a cathode 55e, and a control grid .5512 The two cathodes 55D and 55e are connected through a common cathode resistor 56 to 'the negative supply conductor 35. A voltage dropping resistor 51 is included in the connection of the anode 55a of the first stage valve and of the positive supply conductor 35. The voltage at the anode 55a is divided by a means of a voltage dia .vider which comprises two resistors 58 and 55 which are connected in series between the anode l550i and the negative supply conductor 36. The control grid 551 of the second stage valve is connected to an intermediate point on the voltage divider such that at zero speed of the web the second stage valve is conducting and the relay .44 is energized.

With the foregoing understanding of the ele- .inents and their organization the operation of -the system will readily be understood from the following detailed description. When the printing cylinders and the web are at a standstill, no pulses are supplied to the grid 34e of the rst A stage valve of the web break detecting device and consequently the second stage valve is non- 4conducting and the relay 33 is deenergized. In

stage valve of the speed indicating device. Consequently the second stage valve of the phase inverter A55 is conducting with the result that the operating coil of the relay 44 is energized and the relay is picked up to open its normally closed contacts 44a.

As the printing cylinders and the web are lbrought up to speed, the register indicia I8 passing the web scanning head I0 produce positive voltage pulses which are supplied to the gird 34e. As a result of these positive pulses the conductivity of the rst stage valve is increased and the second stage valveis rendered conducting, and at a predetermined low speed Nl the conduction of the second stage valve is insuilicient to keep the relay 33 picked up and its normally closed contacts remain closed.

At a slightly higher speed N2, the positive voltage pulses supplied from the selector switch mechanism to the grid 45e of the first stage valve of the speed indicating device have sucient frequency to render the second stage valve of the phase inverter nonconducting thereby deenergizing the operating coil of the relay 44. In response to deenergization, this relay drops out and closes its normally closed contacts 44a thereby preparing the alam circuit for completion.

If the web breaks at any speed above N2, no web indicia will pass the web scanning head I0 and no positive voltage pulses will be supplied to the control grid 34e of the rst stage valve of the web break detecting device. As a result, the rst and second stage valves become nonconducting and the operating coil of the relay 33 is deenergized. Responsively to deenergization, the relay 33 drops out and closes its normally closed contacts 33a thereby to complete the alarm circuit 3U which was prepared or partially completed at the speed N2 by the closing of the contacts 44a.

The completion of the alarm circuit 30 causes either a visual or an audible alarm to begiven or it may be utilized to disconnect the press drive motor from its source.

The speed at which the speed indicating relay 44 drops out is determined by the setting of the potentiometer 50.

Although in accordance with the provisions of the patent statutes this invention is described as embodied in concrete form and the principle thereof has been explained together with the best mode in which it is now contemplated applying that principle, it will be understood that the apparatus shown and described is merely illustrative and that the invention is not limited thereto since alterations and modieations will readily suggest themselves to persons skilled in the art Without departing from the true spirit of the invention or fromthe scope of the following claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A web detector for use on a machine having an element operating on a length o'i moving material having a plurality of indicia distributed along its length` comprising, a normally inactive alarm circuit, means responsive to speeds of said element greater than a predetermined speed for preparing said alarm circuit for actuation, and photoelectric means responsive to non-passage of said indicia for actuating said prepared alarm circuit to indicate a break in said length of material.

2. A web break detector for use on a machine having an element operating on a length of moving material having a plurality of indicia distribuiedialoaefitslengtn comprising.; .anomalia open alarm circuit. means respcnsiverto speedscfsaid element;greater `than a predeterminedspeedffor.

partially completing Said alarm circuit,- and pho-V toelec-trc meanslresponsve to nonfpassage of .said indi-cia for completing said alarm circuit.

3, Aweb breakdetector for -use=ona machine having -an element operating vcna length otmov@ nermaterial having. aplurality otindicia distrib uted along.its.lengthcomprsinga-normallycpen alarmcircuit, means responsive to speedsrof said elementgreater-fthan a.,predetermined sneedand 4a relay controlled thereby for-partially completing said ;alarm.circuit,. and plmotoelectric means responsive to -nonfpssge of said .indicia and@ ag, relay ,I controlled. thereby foriv completing said alarm circuit.

4;. Arweb .break detector fornusefonia .machine having an. element.l operatingI on a length of moving. material having a plurality -of indicia distributed along its. length comprising, an alarmI circuit, means responsive to the speed ot said lelement for preparing. said lalarm circuit for actuation.. anampliler comprising a rst stage electric valve. and a second stage electric -valve ea-chprovided with ananode, a cathode and a corrtrol grid, aresistor connected in fthe cathode clrcuitfof .the first st'agefvalve to provide cathode follower operation, a connection from the cathode terminal ot said resistor to the grid of said second stagetvalvef photoelectric means responsiveto the passage ot said s indicia. for supplying successive signal voltage. impulses to the grid of said lirst stage valveto Vincrease the conductivity ofsaid first stage valve during each-of'said impulses, a

capecitonconnectedin parallel with said resistor vforzvarying the conduction of said second stage Valve during. the passage of 'said indicia, andra relay responsive tothe-conditiomof conduction of said second stage -valve during ynon'passage of said indicia forl actuating said prepared alarm circuitzto indicate a lbreak' irl-said length Otmaterial.

5; A`.weblbreak detector forxuse on a machine having an element operating on a length of moving material having a plurality1of vindicia-distributed `alongrits length comprising, an alarm circuit, means responsive .to the speed-of said elementfor preparing saldalarm circuit for-lactuation, an amplifier comprising a first stage electricv valve and a second stage electric valve each provided-with an anode, afcathode andia control grid; means supplyinga biasing voltage to the-grid of said-second stage-Naive -to effectla normal condition of non-conduction of said-second stage valve when said iirs-t stage-valve is nonconducting, a-resistor connected lin thel cathode cir-cuit of said irstfstage valve to provide cathode follower operation, a connection from the cathode lterminal -oflsaid resistor to the grid'lofsa-id second stage valve, photoelectric meansresponsive to the passage ofA said indiciafor -supplyingsuccessive signal voltage impulses tothe grid of said rst stage valve to increase the conductivity of said first stage'valve during each of 'said impulses, acapacitor connected in parallel with said-resister and becoming charged in response Ito conduction ofV said first stagevalveto varythe conduction of said second stage valve, and -a-relay responsive to said normal condition of nonconduction of said second stage valve for-actuating said-prepared alarm circuit -to indicate a break in said length of material.

6. Aweb breakdetector for-use cnav machine having ari-element operating on aflengtho movameno ing nuten-iai.' having` acpluralityrof. indicia disA tributedv along itslength comprisina: arl-.alarm Circuit,v means responsive to the speed oisaid element forvpreparingr said alarmcircuit fior; ac.- tuaticn., an l ampliercomprising.; a.. rst. stage electricI valve and aisecondstage -electrlczvalve each provided with an anode; ac camhode and a control4 grid; means-,biasing said second stage valve to cutoff when said ,first stage valve isfnonconducting, a resstoriconnected in the-cathode circuitiof said first stage valve toproviderlcathode followeroperation, aconnection from fthecathode terminal of said 'resistor -to .the Agrid'gotfsaicl 'sec-'1 ond stage valve, photoelectric means responsive to the passage ofsaid indicia ior'supplying succesf sive signal voltage impulses to the grid of said rststage valve to. rendersaidnrstrstage. valve conducting during eachof said impulses, a ca.,- pacitcrconnected in Vparallel .with said resistor andv becoming charged in response to conduction offsaidfirst stage valve.- to render said second stage/valve conducting, and-a relay responsveto the-cutci condition of said-second stage valve 'for actuating said prepared alarm circuittoindi-cate a-break in said length of material.

7. A web detector for use on amachine having ari-element operatingon a length of movingv ma-4 terial having a plurality of indicia distributed along its length comprising, an alarm circuit, means for partially completingsaid alarm circuit at apredetermined speed of said element comprising means responsive to the speed of said element for producing voltage pulses having a. frequency proportioned to the speed of 'said element, a capacitor, electric valve means responsive to said vvoltage pulses for charging said capacitor, a. discharge, circuit for'said capacitorhaving a re sistance that is relatively high with respect to the resistance of the charging circuit to effect a charge on said capacitor proportional to the frequencyV of said pulses, a relay and an electric valve phasel inverter responsive )to the'charge on said capacitor for effecting operation of said relay at'apredeterminedspeed of said element, and photoelectric means responsive to the non-pam sageof said indicia for actuating said prepared alarm circuit to indicate a break in said .length of material.

8.'. A web detector for use onamachlne hav-il lng an-element operating on a length offmoving material having a plurality of 'indicia distributed along its length comprising, an alarm circuit, means for partiallycompleting said -alarm circuit at'apredeterminedspeed-of said element comprising meansresponsive to the speed of said element for producing voltage pulses having a fre-y quencyproportionedto the speed of fsaid element, alt-capacitor, electric valve means responsive to saidvoltagefpulses for charging :said capacitor, a. discharge,- circuit for said 'capacitorfhaving a Ie sistance that is -relatively high with respect to the resistance of theA charging circuit" to effect a charge on said capacitor proportional #tothe frefluency.. of said `pulses, a. relay': having7 normally closed contacts andan electric valve phase-ini.` verter responsive to the charge on saidfcapacitor for deenergizing said-'relayat ay predetermined speed of said element; and photoelectricmeans -responsive tothe non-passage-of said indicia for actuating-said prepared alarm circuit to indicate -a break in'said length of material.

9. Foruse one machine having a driving motor and an element operating on a length of material provided-with aplurality of-'indlcia distributed alongitslengthl comprising'l arr alarmcircuit,

. ...un Milli-H means responsive only to speeds of said element greater than a predetermined minimum speed for preparing said alarm circuit for actuation, photoelectric means responsive to non-passage of said indicia for actuating said prepared alarm circuit and means responsive to actuation of said alarm circuit for deenergizing said driving motor.

10. For use on a machine having a driving motor and an element operating on a length of moving material having a plurality of indicia distributed along its length comprising a normally open alarm circuit, means responsive only to speeds of said element greater than aA predetermined minimum speed for partially completing said alarm circuit at a predetermined speed of said element, photoelectric means responsive to l0 non-passage of said indicia for completing said alarm circuit, and means responsive to the completion of said circuit for deenergizing said driving motor.

GEORGE B. DUNN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,150,467 Stain Mar. 14, 1939 2,351,229 Potts June 13, 1944 2,430,305 Sheets Nov. 4, 1947 

